Biodegradation pathway of DDT is multistep process in anaerobic environment, involving reductive dechlorination, dioxygenation, hydrogenation, hydroxylation, decarboxylation, hydrolysis (a major transformation pathway in soil and water in the presence of H2O, H+, and OH¯ ), and meta-ring cleavage reactions. Biodegradation pathway of DDT is multistep process in anaerobic environment involving reductive dechlorination such as three degradation step (DDT→DDD,DDE[6]), hydrogenation, dioxygenation, hydroxylation, decarboxylation and meta-ring cleavage reactions(Rangachary and others, 2012). That is different from the degradation pathways for anaerobic biodegradation but high-order metabolites such as DDA, DDOH[7] and DDNU (Aislabie and others, 1997). (Wedemeyer, 1967), reported first metabolic pathways for DDT by aerobacter aerogenes that shown at the bottom:

Researches were lack of information about DDT degradation. Later, (Planche and others, 1979) indicted DDE could be degraded to DDMU by a microcosm under anaerobic sediments.biodegradation pathway in sediment shown on figure 2. DDT and its metabolites in the sediment:

It is not readily biodegraded but it is transformed biologically in both situations aerobic and anaerobic, mainly to the stable heptachlor epoxide (Lichtenstein and others, 1970). (Hayashi and others, 2013) , have reported that heptachlor was degraded a small amount to heptachlor epoxide in soil. Figure3 shown this degradation pathway.

Of the year 1960s began studies on biodegradation of endrin and dieldrin that more researches were reported about the aerobic biodegradation (Matsumoto and others, 2009). Biodegradation of dieldrin and endrin was reviewed in 2007 and 1982 (Lal and Saxena, 1982; Matsumoto and others, 2009). (GOWDA and Sethunathan, 1977), studied that endrin proceeded under anaerobic conditions in three soils by radiotracer technique. Thay have reported anaerobic microbial strains could degrade various types of POPs such as ,heptachlor, dieldrin, aldrin, endrin and HCB. These strains isolated from PCB-contaminated sediment. (Baczynski and others, 2004), reported that methanogenic granular sludge could dechlorination of cyclodiene pesticides such as dieldrin and endrin.(Baczynski and others, 2004), studied methanogenic granular sludge with purpose dechlorinate dieldrin and endrin. Biodegradation studies under anaerobic conditions are summarized in Table 2.

Deldrin has simple mechanism reported by (Maule and others, 1987) that is the deletion of the chlorine atom from chlorinated hydrocarbon. (Chiu and others, 2005), reported cleaving the epoxide ring by a mechanism of epoxide reduction by anaerobic enrichment culture obtained from river sediment. So, they are the Transformation of deldrin to aldrin then aldrin is converted to two syn- and anti-monodechlorodieldrin metabolites by epoxide reduction. Researches show only two monochlorinated metabolites of endrin under anaerobic transformation so it can say bacteria have a catalyzed role in reductive dehalogenation (Matsumoto and others, 2009).

the mechanism of biotransformation of HCH-isomer and lindane under anaerobic condition is explained with detection of intermediates substance of the presumed pathway. According to papers and reports, intermediates of HCH such as TeCCHs[14], PeCCHs[15] , PCCHa[16] (Buser and Mueller, 1995). (Tsukano and Kobayashi, 1972), abserved TeCCH ï¬‚ooded rice ï¬eld soils treated with lindan but this intermediates was not found in soils treated with sodium azide or in soils without lindane treatment. suggested two degradation pathway for HCH isomers under anaerobic conditions, Based upon identify the intermediates material

Methoxychlor [1,1,1-trichloro-2,2-bis(p-methoxyphenyl) ethane] is a hazardous substance and stable for this reason, is one of POPs. Methoxychlor have a half-life &lt; less than 28 days under anaerobic conditions in sediments also in soils. (Satsuma and Masuda, 2012), this paper to studied seven bacteria that ability to dechlorinate methoxychlor in aerobic and anaerobic conditions. This seven environmental bacterial species including: Enterobacter amnigenus, Aeromonas hydrophila, Bacillus subtilis,Klebsiella terrigena, Mycobacterium obuense, Acinetobacter calcoaceticus, and Achromobacter. Biodegradation studies of OCPs under anaerobic conditions are summarized in Table 2.

Microbial species and pathway dechlorination of methoxychlor in the environment are not well-known or there are few reports (Castro and Yoshida, 1971; Masuda and others, 2011b). Enterobacter aerogenes were capable of degrading methoxychlor to DMDD [19] under anaerobic conditions (Mendel and Walton, 1966). Eubacterium limosum is a bacteria from human intestine that has been able degrades of methoxychlor to 1,1-dichloro-2,2-bis(pmethoxyphenyl) ethane (methoxydichlor) (Yim and others, 2008). Also, K. pneumoniae converts methoxychlor to [1,1-dichloro-2,2-bis(4-methoxyphenyl)ethane, de-Cl-MXC] (Baarschers and others, 1982).

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